As spring approaches and warmer weather beckons, Rick Lovett looks at the science of training for hot-weather performance, and also explains why and how heat training can benefit your performance ALL year round MORE
Humidity and Performance
I am an aged veteran sprinter, a poor stayer at any distance beyond 200m. I am often to be found trying to run a slow mile. However, my experiences might show up factors that apply to the top runners too, although they may not be aware of them.
Take the recent London Marathon, in which amazing results were produced all over the place. In the men’s race, the top five chalked up many records between them and all did personal bests. The two top two or three in the women’s race, too, and even the wheelchair athletes.
‘Good conditions’ were said to be the cause.
Of course they were, surely, as nothing else had changed. Disley hadn’t gone around shortening the roads, the Hale-Bopp comet’s influence had to be ruled out. So what good conditions were there that affected all and sundry?
There were certainly good weather conditions. Perhaps that could have explained it. But what exactly, that could be measured? There was a good temperature, warm for April, yet not a heatwave. No rain, no wind. But what was special that produced such results and how do you measure it?
I’ll tell you what I think. Some days when I go out running I get the feeling from the start that things are ideal, and I run at my best, poor though it is. It’s something in the air. It happens when there’s a crispy day, with a dry feeling to the air, and my home hygrometer confirms it. It was like that on the London Marathon Sunday – and measurably so: the relative humidity WAS amazingly low (and the barometer high, 305), not only on my home meter but on the official one. That’s what made it so runnable, that’s where the advantage must have come from.
I theorise like this to explain its workings: with low humidity there’s less water vapour in each bucketful of air – and consequently more ‘pure’ air available for running on.
A sprinter like me in particular needs every suck of oxygen he can get from each lungful. It may not make such a critical difference to real runners as it does to me, but difference it must make. It may give them only a one per cent advantage, but, dash it all, one per cent of 2 hours 10 is more than a minute, enough to provide a personal best for such as McColgan, Pinto and the rest.
Is this effect known to science?
Owen Anderson replies:
The relationship between humidity and performance has been little studied by the people in white coats. At first glance, it would seem that dry, less dense air would decrease the work of the diaphragm and intercostal muscles, which must ‘pull’ air into the lungs. On the other hand, the system works by pressure differences. For inhalation, the diaphragm descends into the abdominal cavity, trying to create an area of low pressure in the chest. The denser the outside air, the more quickly it should rush into the chest cavity. In that sense, humidity would seem to be a positive. The outflow scenario wouldn’t be different, since air is almost completely saturated with moisture anyway after it has been in the lungs – on dry or humid days.
The ‘crowding’ possibility you mention (oxygen being shoved aside by water molecules) is an interesting one. It has always been assumed that it has little direct impact, but perhaps there’s something to it. The argument against it is that air coming into the lungs is 21 per cent oxygen, while air going out is about 16 per cent. Therefore there is ‘surplus’ oxygen (the blood take-up is only about 25 per cent of what is present) and a little extra water blocking some of the oxygen molecules shouldn’t be a problem.
Of course, the really big positive of dry air is that it promotes cooling. Evaporation rates are much higher on dry days, the skin becomes an excellent cooling device, and – since body temperature remains temperate – less blood must be transported to the skin for cooling, leaving more of it for the muscles.